Measuring and Controlling the Energy Spread in CEBAF

As compared to electron storage rings, one advantage of recirculating linear accelerators is that the beam properties at target are no longer dominated by the equilibrium between quantum radiative diffusion and radiation damping because new beam is continually injected into the accelerator. This allows the energy spread from a CEBAF-type machine to be relatively small; the measured energy spread from CEBAF at 4 GeV is less than 100 parts per million accumulated over times of order several days. In this paper, the various subsystems contributing to the energy spread of a CEBAF-type accelerator are reviewed, as well as the machine diagnostics and controls that are used in CEBAF to ensure that a small energy spread is provided during routine running. Examples of relevant developments are (1) stable short bunches emerging from the injector, (2) precision timing and phasing of the linacs with respect to the centroid of the beam bunches on all passes, (3) implementing 2 kHz sampling rate feedback systems for final energy stabilization, and (4) continuous beam energy spread monitoring with optical transition radiation devices. We present measurement results showing that small energy spreads are achieved over extended periods.Comment: 5 pages, 5 figures, Invited Paper TH205 at 2000 International Linac Conferenc

Последний из «могикан» советского библиотековедения. (К 90-летию памяти профессора А. А. Халафова)

The founder of library science in Azerbaijan “The founder of library science in Azerbaijan”, Abuzar Aly oglu Khalafov was born on December 25, 1931, in the village of Jil, located on the territory of Goych in Western Azerbaijan. In 1938–1945 he studied at a seven-year general education school, in 1945–1946 he worked on the collective farm named after Ali Bairamov. From 1950–1955 he studied at the library department of the Faculty of Philology of the Azerbaijan State University. Over the years, he worked as a teacher, senior lecturer, associate professor at the Library Faculty. In 1961 he defended his candidate’s thesis on the topic “From the history of librarianship in Azerbaijan” (1920–1932)”, and in 1975 he defended his doctoral dissertation on the topic “From the history of librarianship in Azerbaijan” (1933–1958). In 1978 he became a professor. These works, being significant and relevant, reflected the dynamics of the development of librarianship in Azerbaijan. He scientifically substantiated the goals and objectives of library activities, and carefully studied its pressing problems, and proposed his own ways to solve them. Abuzar Khalafov was the first to be awarded the degree of Doctor of Historical Sciences in library science. The authors emphasize the role of the prominent scientist in the scientific, pedagogical and cultural life of Azerbaijan by providing numerous examples. Abuzar Khalafov devoted seventy years of his s life to the librarianship of his country.Абузар Алы оглу Халафов – основоположник библиотековедческой мысли в Азербайджане – родился 25 декабря 1931 г. в селении Джил, расположенном на территории Гейча Западного Азербайджана. В 1938–1945 гг. обучался в семилетней общеобразовательной школе, в 1945–1946 гг. работал в колхозе им. Али Байрамова. 1950–1955 – годы обучения на библиотечном отделении филологического факультета Азербайджанского государственного университета. В разные годы Абузар Халафов работал преподавателем, старшим преподавателем, доцентом на библиотечном факультете. В 1961 г. защитил кандидатскую диссертацию «Из истории библиотечного дела в Азербайджане» (1920–1932 гг.)», а в 1975 г. – докторскую диссертацию «Из истории библиотечного дела в Азербайджане» (1933–1958 гг.). В 1978 г. стал профессором. Эти значимые и актуальные работы отражали динамику развития библиотечного дела в стране. Учёный научно обосновал цели и задачи библиотечной деятельности, тщательно изучил актуальные проблемы и предложил варианты их решения. Абузар Халафов стал первым, кто удостоился степени доктора исторических наук в области библиотековедения. В статье представлена роль учёного в научной, педагогической и культурной жизни Азербайджана. 70 лет своей жизни учёный посвятил библиотечному делу страны

Production of highly-polarized positrons using polarized electrons at MeV energies

The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-$Z$ target. Positron polarization up to 82\% have been measured for an initial electron beam momentum of 8.19~MeV/$c$, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.Comment: 5 pages, 4 figure

Magnetized Electron Source for JLEIC Cooler

Magnetized bunched-beam electron cooling is a critical part of the Jefferson Lab Electron Ion Collider (JLEIC). Strong cooling of ion beams will be accomplished inside a cooling solenoid where the ions co-propagate with an electron beam generated from a source immersed in magnetic field. This contribution describes the production and characterization of magnetized electron beam using a compact 300 kV DC high voltage photogun and bialkali-antimonide photocathodes. Beam magnetization was studied using a diagnostic beamline that includes viewer screens for measuring the shearing angle of the electron beamlet passing through a narrow upstream slit. Correlated beam emittance with magnetic field at the photocathode was measured for various laser spot sizes. Measurements of photocathode lifetime were carried out at different magnetized electron beam currents up to 28 mA and high bunch charge up to 0.7 nano-Coulomb was demonstrated

High Current High Charge Magnetized and Bunched Electron Beam From a DC Photogun for JLEIC Cooler

A high current, high charge magnetized electron beamline that has been under development for fast and efficient cooling of ion beams for the proposed Jefferson Lab Electron Ion Collider (JLEIC). In this paper, we present the latest progress over the past year that include the generation of picosecond magnetized beam bunches at average currents up to 28 mA with exceptionally long photocathode lifetime, and the demonstrations of magnetized beam with high bunch charge up to 700 pC at 10s of kHz repetition rates. Detailed studies on a stable drive laser system, long lifetime photocathode, beam magnetization effect, beam diagnostics, and a comparison between experiment and simulations will also be reported. These accomplishes marked an important step towards the essential feasibility for the JLEIC cooler design using magnetized beams

Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering

We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 = 0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state, and generally agree with calculations with significant inelastic hadronic intermediate state contributions. A_n provides a direct probe of the imaginary component of the 2-gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.Comment: 5 pages, 3 figures, submitted to Physical Review Letters; shortened to meet PRL length limit, clarified some text after referee's comment

Strange Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment

We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < Q^2 < 1.0 GeV^2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange quark contributions to the currents of the proton. The measurements were made at JLab using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate non-zero, Q^2 dependent, strange quark contributions and provide new information beyond that obtained in previous experiments.Comment: 5 pages, 2 figure

Production of Magnetized Electron Beam from a DC High Voltage Photogun

Bunched-beam electron cooling is a key feature of all proposed designs of the future electron-ion collider, and a requirement for achieving the highest promised collision luminosity. At the Jefferson Lab Electron Ion Collider (JLEIC), fast cooling of ion beams will be accomplished via so-called \u27magnetized cooling\u27 implemented using a recirculator ring that employs an energy recovery linac. In this contribution, we describe the production of magnetized electron beam using a compact 300 kV DC high voltage photogun with an inverted insulator geometry, and using alkali-antimonide photocathodes. Beam magnetization was assessed using a modest diagnostic beamline that includes YAG view screens used to measure the rotation of the electron beamlet passing through a narrow upstream aperture. Magnetization results are presented for different gun bias voltages and for different laser spot sizes at the photocathode, using 532 nm lasers with DC and RF time structure. Photocathode lifetime was measured at currents up to 4.5 mA, with and without beam magnetization